AT&T Wireless has announced a small but significant increase in revenue in the third quarter, largely due to the iPhone. The company saw revenues rise 15 percent over revenues from the same time last year, translating into a net income of $12.6 bllion. They also saw 2.4 million activations of the iPhone, nearly half of which were new customers.

“I am particularly pleased with the customer response to the iPhone 3G,” Randall Stephenson, AT&T’s chairman and CEO, said in a statement. “We’re expanding the market, as users adopt more data and media-rich services and access a wide array of applications.”

Unfortunately, a drop in wireline revenue has all but offset the increased revenue generated by AT&T Wireless and the iPhone. The company says wireline revenues dropped 2 percent from last year at this time. This isn’t surprising given that more and more people are dropping their landlines in favor of cell phones or VOIP services. Most telecom carriers are seeing similar drops in wireline revenues.

Whether the fourth quarter brings similar gains for AT&T’s wireless division remains to be seen. The rocky economy and new offerings from Sprint and Blackberry may very well give them a run for their money.